1. Field of the Invention
The invention relates to an exhaust gas purifying apparatus that purifies exhaust gas discharged from an engine, and a method thereof.
2. Description of the Related Art
Exhaust gas discharged from an engine, which is mounted on a vehicle and the like, contains HC, CO, and NOx. A three-way catalyst, a NOx storage reduction (NSR) catalyst or the like is provided in an exhaust passage in order to remove these substances.
For example, Japanese Patent Application Publication No. JP-A-2000-282844 describes a method for purifying exhaust gas containing hydrocarbon compounds, which mainly consist of methane. In the method, ozone is generated and supplied into high-temperature exhaust gas, whereby the hydrocarbon compounds are removed from exhaust gas.
As described above, for example, ozone is used to remove the hydrocarbon compounds. However, for example, when the ozone is supplied directly into exhaust gas discharged from the engine to remove these hydrocarbon compounds as described in the above publication, NOx and the like contained in exhaust gas may be oxidized by the ozone that has strong oxidizability. That is, an oxidation reaction may occur. In such a case, ozone is not appropriately used in removing the hydrocarbon compounds. Further, because NOx should be removed by a reduction reaction using a three-way catalyst or the like, the oxidation reaction, which is reverse of the reduction reaction, may make it difficult to remove NOx.